- BMI: 6-7 years: less than or equal to 19 kg/m2, 8-9 years: less than or equal to 20 kg/m2, 10-11 years: less than or equal to 22 kg/m2, 12-13 years: less than or equal to 24 kg/m2 and 14-17 years: less than or equal to 27 kg/m2.